Signaling by Mycobacterium tuberculosis Is Associated with Reduced Phagosome–Lysosome Fusion and Increased Survival within Human Macrophages

Complement receptor (CR)-mediated phagocytosis of Mycobacterium tuberculosis by macrophages results in intracellular survival, suggesting that M . tuberculosis interferes with macrophage microbicidal mechanisms. As increases in cytosolic Ca 2 1 concentration ([Ca 2 1 ] c ) promote phagocyte antimicrobial responses, we hypothesized that CR phagocytosis of M . tuberculosis is accompanied by altered Ca 2 1 signaling. Whereas the control complement (C)-opsonized particle zymosan (COZ) induced a 4.6-fold increase in [Ca 2 1 ] c in human macrophages, no change in [Ca 2 1 ] c occurred upon addition of live, C-opsonized virulent M . tuberculosis . Viability of M . tuberculosis and ingestion via CRs was required for infection of macrophages in the absence of increased [Ca 2 1 ] c , as killed M . tuberculosis or antibody (Ab)-opsonized, live M . tuberculosis induced elevations in [Ca 2 1 ] c similar to COZ. Increased [Ca 2 1 ] c induced by Ab-opsonized bacilli was associated with a 76% reduction in intracellular survival, compared with C-opsonized M . tuberculosis . Similarly, reversible elevation of macrophage [Ca 2 1 ] c with the ionophore A23187 reduced intracellular viability by 50%. Ionophore-mediated elevation of [Ca 2 1 ] c promoted the maturation of phagosomes containing live C-opsonized bacilli, as evidenced by acidification and accumulation of lysosomal protein markers. These data demonstrate that M . tuberculosis inhibits CRmediated Ca 2 1 signaling and indicate that this alteration of macrophage activation contributes to inhibition of phagosome–lysosome fusion and promotion of intracellular mycobacterial survival.